This invention relates to devices for separating particulate materials of varying specific gravities. In another aspect, this invention relates to a device for separating particles of relatively high specific gravity from particles of relatively low specific gravity wherein both kinds of particles are carried in temporary suspension by a fluid. In still another aspect, this invention relates to a device for separating particulate materials of varying specific gravity which includes a truncated conical surface having a series of concentric stepped indentations wherein each of the indentations includes two surfaces joined at a 90.degree. angle.
It is a well known principle that particulate matter of varying specific gravity may be separated by placing the particulate materials is a carrier fluid and thereafter creating a permanent or temporary suspension. Depending upon the carrier fluid employed and the degree of variance of the specific gravities of the particulate materials to be separated, separation can be effected in various manners. For example, it is sometimes possible to employ a carrying fluid having a specific gravity greater than that of a portion of the particulate matter to be separated and less than that of another portion of the particulate matter. In these cases, separation can be effected relatively easily since the particulate matter of lower specific gravity simply floats on the surface of the carrying fluid and can be skimmed off. In other instances, it is impractical to use such a carrier fluid and therefore an inexpensive and readily available carrying fluid is employed even though all of the particulate materials which are to be separated have specific gravities greater than the carrying fluid. In these cases separation can be effected by imparting motion to the carrying fluid in order to temporarily suspend those portions of the particulate matter which have a relatively low specific gravity. Separation can then be effected by separating the fluid medium with the suspended particles of relatively low specific gravity from the particles of relatively high specific gravity which were not carried into suspension by the motion imparted to the carrier fluid.
A well known application of this latter method of separation is the practice of panning for gold. It was discovered very early that particles of gold could often be found mixed with the sand and other particulate material found in stream and river beds. Early prospectors utilized the above discussed principles of separation by specific gravity to separate the valuable gold particles from the sand, mud and other materials found in the stream bed. Because water was readily available as the carrier fluid, the separation process was effected by simply placing particulate matter from the stream bed in a container along with a sufficient amount of water and imparting motion to the water to thereby suspend the particles of relatively low specific gravity and separate them from gold particles which have a relatively high specific gravity. Gold has a specific gravity in the range of from about 16 to about 18 grams per cubic centimeter while sand normally has a specific gravity of 2.5 grams per cubic centimeter. This wide discrepancy in specific gravities made it possible to separate the gold particles from sand and other particulate matter by swirling the mixture in a simple pan device and pouring the water and suspended sand particles out of the pan leaving the high density gold particles behind.
This method of gold recovery has some inherent disadvantages. For example, when the gold particles are of relatively low particle sizes, they sometimes will follow the sand and other particulate matter into suspension upon swirling in a pan type device. When this occurs, pouring of the suspended materials out of the gold pan will result in a loss of these fine particles of gold. Such losses of finely divided gold particles have heretofore been unavoidable because of the inaccuracies and human error which are inherent in the panning of gold by hand. The amount of swirling motion imparted to the water is incapable of being finely adjusted so as not to cause gold particles of small particle size to be placed in suspension when it is performed by hand. Furthermore, the water carrying the suspended particles must be poured out of the pan at a rate sufficient to keep the suspended particles from falling out of suspension and becoming recombined with the gold particles in the bottom of the pan. Thus, the rates of swirling and pouring are subject to the inaccuracies of human judgment and present a problem in the recovery of gold particles of relatively small particle sizes. A device which is capable of use in this relatively simple method of gold recovery, but which aids in the recovery of gold particles of relatively small particle size is therefore desirable.